------- PIL real; default = 1005.0; group 9
CP1 is a PIL variable used for specifying the specific heat at constant pressure of the phase-1 material. It is employed within PHOENICS for deducing temperature from enthalpy, or vice versa.
The text-book definition of specific heat is that it is the rate of change of enthalpy with temperature; but PHOENICS makes use of a non-standard definition described here.
The difference of definition is important only when specific heat varies with temperature.
The default value of CP1 is that pertaining to air at standard pressure and temperature.
Thus:
Such values can be prescribed in the usual ways, namely via:
It is Method 2 i,e, the use of the built-in formulae, which will now be described.
In these formulae, the absolute temperature, Tabs, is equal to the local temperature, TEM1, plus the constant, TEMP0, which is set in the Q1 file.
It should be remarked that the built-in formulae are rather unsophisticated. Users are recommended to use the In-Form method for introducing specific-heat information of any complexity.
This implies that the enthalpy is a quadratic function of temperature.
This implies that the enthalpy is a cubic function of temperature.
For air (280-1500K): A= 917.; B= 0.258; C=-3.98E-5
For ammonia gas (300-1000K): A= 1520.; B= 1.94; C=-1.79E-4
This also implies that the enthalpy is a cubic function of temperature.
For CO2 (300-3500K): A= 1540.; B=-3.45E5; C= 4.14E7
For O2 (300-5000K): A= 1420.; B=-2.73E4; C= 4.94E7
For N2 (300-5000K): A= 1420.; B=-2.88E5; C= 5.35E7
Note that the integration is carried out from Tabs=200 upward, because the Cp expression cannot be integrated down to Tabs=0
where CP1C = Tabs_phase_change, and PHNH1A = latent heat of phase change The latent heat is released over a 1 degree temperature range.
If PHNH1B is not equal to zero, the phase change occurs at constant temperature.
Thus, each of the gases may have its own constant specific heat; so the specific heat of the mixture may depend on composition (alone).
However, PLANT has, for several years, allowed users to express their requirements by way of expressions placed in the Q1 file, where after the GROUND coding has been automatically created.
Now (early 2001) In-Form has extended the facility for placing formulae in the Q1 file, and dispensed with the GROUND-coding feature entirely.
If STORE(CP1) or STORE(SPH1) appears in Q1, then the specific heat will be placed in a 3D store and will be available for printing in RESULT and plotting with PHOTON from PHI.
In GROUND, the integer index ISPH1 should be used in calls to FN routines or as the argument of L0F.
See also PHENC entries, SPECIFIC HEATS and TEM1.
wbs